1. Field of the Invention
This invention relates to a press forming process for bending a sheet metal workpiece to obtain a curved elongate channel-shaped article such as an automobile frame while removing wrinkles which have been formed on the surface of the workpiece in a previous bending process.
2. Description of the Prior Art
In connection with press forming processes for automobile frames and the like, a so-called edge bending process is carried out to bend a flat elongate workpiece into a curved elongate workpiece prior to a press forming process to obtain a curved elongate channel-shaped frame. It is to be noted that wrinkles are inevitably formed on the surface of the workpiece in the edge bending process. These wrinkles not only remain unremoved after the press forming process on the surface of the workpiece, but also give rise to problems in which wear of press dies at portions corresponding to the wrinkles of the workpiece is promoted thereby causing galling and seizure of the press dies.